The therapeutic value of peptide prodrugs and peptidomimetics have gained increasing attention from the pharmaceutical industry. The intestinal uptake of many of these drugs is mediated by the dipeptide transporter, which has recently been cloned from a number of species. With the advent of novel prodrug approaches to oral drug delivery, a growing demand exists for a convenient screening system for assessing the permeability of potential orally delivered prodrug candidates. Current in vivo systems measuring drug permeabilites through animal and human studies are cumbersome and not cost effective. Current in vitro tissue culture systems using Caco-2 and/or HT29 cells, which mimic the absorptive and mucin-producing cells in the small intestine, respectively, are not suitable as a screening assay for peptide prodrug and peptidomimetic drug permeability, since the cells express the dipeptide transporter at low levels thereby resulting in lower effective permeability estimates for the carrier-mediated compounds. Using novel adenoviral and non viral strategies, we propose to overexpress the dipeptide transporter in a Caco-2/HT-29 coculture tissue culture system and develop an reproducible in vitro screening assay for peptide prodrugs and peptidomimetics. The system would be characterized by reproducibility and cost-effectiveness and as such could have significant commercial application. PROPOSED COMMERCIAL APPLICATION: Prodrug strategies are an effective means of increasing oral bioavailability in a large class of compounds that may otherwise not be utilized because of poor intestinal permeability. An effective screening system which aids in rationale drug design at the early stages of the discovery phase of drug development would be an extremely useful tool. Further, the proposed screening system is flexible and could be used for other transporters along with the dipeptide transporter. Thus, the system, if successful, will have broad applicability to novel drug delivery strategies.